In gas turbine aeronautical engines, the improvement of efficiency and reduction of certain polluting emissions leads to the search for and operation at increasingly higher temperatures. In the case of entirely metal turbine ring assemblies, it is necessary to cool all the elements of the assembly and in particular the turbine ring which is subjected to very hot flows. The cooling of a metal turbine ring requires the use of a large quantity of cooling air, which has a significant impact on the performance of the engine since the cooling flow used is taken from the main flow of the engine.
The use of ring segments made of CMC material has been proposed in order to limit the ventilation necessary to the cooling of the turbine ring and thus increase the performance of the engine.
However, even if ring segments made of CMC are used, there is still a need to use a significant quantity of cooling air. The turbine ring is, in fact, confronted with a hot source (the duct in which the hot gas flow flows) and a cold source (the cavity delimited by the ring and the casing, hereinafter designated by the expression “ring cavity”). The ring cavity has to be at a higher pressure than that of the duct in order to avoid gas originating from the duct returning to this cavity and burning the metal pieces. This pressurization is obtained by taking “cold” air at the compressor, which has not passed through the combustion chamber, and routing it to the ring cavity. Maintaining such a pressurization therefore makes it impossible to totally cut off the supply of “cold” air from the ring cavity.
Furthermore, studies conducted by the Applicant have shown that a ring, made of CMC or metal material, cooled by known cooling systems, can exhibit detrimental thermal gradients which generate unfavourable mechanical stresses. In addition, the cooling technologies used for a metal ring cannot easily be transposed to a ring made of CMC material.
Whatever the nature of the material implemented for the ring segments, it would therefore be desirable to refine the existing cooling systems in order to limit the unfavourable thermal gradients in the cooled ring segments and therefore the generation of unfavourable stresses. It would, in addition, be desirable to refine the existing cooling systems in order to optimize the quantity of cooling air actually used for the cooling of the ring by limiting in particular the leaks of cooling air.
The invention aims specifically to address the abovementioned needs.